1. Field of the Invention
The present invention relates to a mobile terminal and, more particularly, to an apparatus and method for controlling power amplification in a mobile terminal.
2. Description of the Background Art
In general, a mobile communication terminal is an equipment by which a user can communicate with another party. Such mobile communication terminals may include but are not limited to cellular telephones, Personal Digital Assistants (PDAs), etc. As the mobile terminal is wirelessly connected to a mobile base station of a pertinent service area, it can maintain a communication state even while moving.
A mobile communication network is wirelessly connected to the mobile terminal through a base station and checks a moving direction of the mobile terminal on a real time basis. The base station keeps checking how far the terminal is, in order to maintain a constant communication sensitivity between itself and the mobile terminal. At the side of the mobile terminal, in order to maintain the constant communication sensitivity, the mobile terminal should maintain a constant power level for a radio frequency signal outputted from an antenna.
Referring to FIG. 1, the output power of the mobile terminal is the power of a radio frequency signal radiated through the antenna of the mobile terminal to the base station. A related apparatus for controlling output power of a mobile terminal includes a radio frequency generating source 6 for generating a radio frequency signal corresponding to a data signal to be transmitted, a power amplifier module (PAM) 5 for amplifying power of a radio frequency signal generated by the radio frequency generating source 6, a coupler 4 for detecting the power amplified by the PAM 5, and an antenna switch 3 for selecting a radio frequency signal (e.g., a TX signal) outputted from the coupler 4 or a reception signal (e.g., an RX signal) received from the antenna 1.
There may also be included a mobile switch 2 for applying the frequency signal selected by the antenna switch 3 to the antenna (ANT) 1, a controller 8 for generating a reference power value for controlling power of the radio frequency signal radiated through the ANT 1, and a comparator 9 for comparing the reference power value generated by the controller 8 and the power value of the radio frequency signal outputted from the coupler 4 and applying a difference value corresponding to the comparison result to the PAM 5. The PAM 5 amplifies power of the radio frequency signal generated by the radio frequency generating source 6.
Accordingly, the radio frequency generating source 6 generates a frequency signal corresponding to a data signal to be transmitted, and applies the generated radio frequency signal to the PAM 5. The PAM 5 amplifies power of the radio frequency signal applied from the radio frequency generating source 6 by a certain amplification factor and outputs the amplified radio frequency signal to the coupler 4. The certain amplification factor is determined by a difference value applied from the comparator 9. This difference value is a rate for amplifying power of the radio frequency signal generated by the radio frequency generating source 6.
The coupler 4 applies the radio frequency signal with the amplifier power received from the PAM 5 to a non-inversion terminal (+) of the comparator and to the antenna switch 3. The antenna switch 3 applies the radio frequency signal received from the coupler 4 to the mobile switch 2 according to a control signal of the controller 8, and applies a reception signal wirelessly received from the antenna to a receiving unit 7.
The mobile switch 2 transfers wirelessly the radio frequency signal outputted from the antenna switch 3 to the base station through the antenna 1. The controller 8 generates a reference power value and applies the reference power value to an inversion terminal (−) of the comparator 9. The reference power value is a value previously set in the controller 8, and the PAM 5 generates power corresponding to the reference power value.
The comparator 9 compares the reference power value applied from the controller 8 and the power value applied from the coupler 4, and applies a difference value corresponding to the comparison result as a power control signal (e.g., an APC) to the PAM 5. For example, the PAM 5 controls an amplification factor of the power of the radio frequency signal generated by the radio frequency generating source 6 on the basis of the difference value so that the power value of the radio frequency signal applied to the coupler 4 can be the same as the reference power value.
Unfortunately, the related apparatus for controlling output power of a mobile terminal has the following problems. A power loss is generated due to supplementary devices attached to the mobile terminal or due to user's contact with the mobile terminal and a user. Also, a power loss generated by the circuits (the mobile switch, the antenna switch, the coupler or the like) of the mobile terminal, and a power loss generated due to a mismatching between the antenna 1 and the mobile switch 2 destabilize the output power of the radio frequency signal radiated from the antenna of the mobile terminal. In addition, because the output power is unstable, the communication sensitivity of the mobile terminal with respect to the mobile communication system is degraded and thus speech quality suffers.
As such, methods and systems are needed to overcome the above-stated problems.